Although the major goal of the Epidemiology Section is the development of a vaccine against Group (Gp) A rotavirus, it is essential to develop reagents for study of other groups of rotaviruses (B-F) since 2 of these groups, B and C, have also been implicated as etiologic agents of diarrheal disease in humans in Asia. It is not known whether non-group A rotaviruses will emerge as important world-wide pathogens after vaccines for Gp A are used extensively. Strategies for cloning genomic RNA of unknown sequence were developed using the fourth gene of Gp A rotavirus strain 69M as a model. cDNA libraries of a porcine Gp C strain and a human Gp C rotavirus isolate were generated and several partial clones specific for different genomic segments from porcine or human Gp C rotavirus were selected and sequenced. Using this sequence information coupled with the polymerase chain reaction (PCR) amplification technique, it was possible to generate complete gene 8 clones from both human and porcine Gp C rotaviruses and obtain evidence this Gp C gene encodes the outer capsid protein VP7, a major protective antigen. In addition, analysis of the genetic relatedness of porcine and human Gp C rotaviruses indicated that these viruses are closely related genetically and quite distinct from Gp A rotaviruses. However, it appears that the porcine and human Gp C rotaviruses evolved from a common ancestral source.